The present invention relates to a fuel injection controller for an internal combustion engine, and more specifically, to a fuel injection controller for internal combustion engines including a passage injector for injecting fuel into an intake passage and an in-cylinder injector for injecting fuel into a combustion chamber.
Japanese Patent No. 3060960 (Japanese Laid-Open Patent Publication No. 10-103118) describes an internal combustion engine provided with a passage injector for injecting fuel into an intake passage (for example, an intake port) and an in-cylinder injector for injecting fuel into a combustion chamber. The passage injector and in-cylinder injector allocate and inject fuel as necessary.
Even in this internal combustion engine, air-fuel ratio feedback control is performed similar to conventional internal combustion engines provided with a single injector. In air-fuel ratio feedback control, the amount of injected fuel is corrected using a feedback correction value, which changes according to the air-fuel ratio, so as to have the air-fuel ratio approach a target value. That is, the amount of fuel injected by the passage injector and the amount of fuel injected by the in-cylinder injector are corrected by the feedback correction value such that the air-fuel ratio approaches a target value in the internal combustion engine.
When fuel is allocated and injected by the passage injector and in-cylinder injector, less fuel is injected by one injector than when fuel is injected by a single injector. Accordingly, the amount of fuel injected by each injector may be less than an allowable lower limit due to the correction performed using the feedback correction value. The allowable lower limit value represents the minimum value of the quantity of injected fuel that can be accurately controlled and is determined in accordance with the injector.